Cellulosic materials such as a paperboard, a boxboard, a cardboard or a chipboard consists of relatively thick, compared with paper, sheet materials that are comprised of bonded, small discrete fibers comprising cellulose. Such fibers are typically held together by secondary bonds that, most probably, are hydrogen bonds. To form a cellulosic sheet, fiber is formed into a rough web or sheet on a fine screen from a water suspension or dispersion of fiber and is combined with fiber additives, pigments, binder material, secondary binder materials or other components. After the sheet is formed on a fine screen, the rough sheet is then dried, calendared and further processed to result in a finished sheet having a controlled thickness, improved surface quality, one or more coating layers, a fixed moisture content, etc. Further, after sheet formation the paperboard can be further coated, embossed, printed or further processed before rolling and distribution. Paperboard, boxboard, chipboard or cardboard typically has a caliper (thickness) of greater than about 0.30 mm (in the united kingdom greater than about 0.25 mm). Paper with a basis weight (grammage) generally above 250 g-m.sup.-1 (51 lbs-10.sup.3 ft.sup.-2) is considered paperboard under ISO standards. Typically, paper is considered a sheet-like material having a thickness of less than about 0.25 mm, often less than 0.1 mm.
Paperboard, boxboard, chipboard and cardboard are made in many types and grades to service a variety of uses. The final finishes of paperboard can be rough or smooth, can be laminated with other materials, but are typically thicker, heavier and less flexible than conventional paper materials. Paperboard can be made both from primary sources of fibers and from secondary or recycled fibrous materials. The fiber used in making paperboard largely comes directly from the forestry industry. However, increasingly paperboard is made from recycled or secondary fiber derived from paper, corrugated paperboard, woven and nonwoven fabric, and similar fibrous cellulosic materials. Such recycled fibrous material inherently contains finishing material such as inks, solvents, coatings, adhesives, residue from materials the fiber source contacted and other sources of contamination. These recycled finishing materials in addition to freshly applied finishing materials contain residual volatile organics that can pose some threat of contamination to the stored contents of containers made from such recycled materials.
The main components used in the manufacture of paper products are mechanical/semi-mechanical wood pulp, unbleached Kraft chemical wood pulp, white chemical wood pulp, waste fiber, secondary fiber, non-wood fibers, recycled woven and non-woven fibers, fillers and pigments. Many varieties of wood pulp used are derived from both hard and softwoods. The chemical properties and composition of paperboard are determined by the types of fibers used and by any non-fiber substances incorporated in or applied on the surface of the paper during paper making or subsequent paper converting operations. Paper properties that are affected directly by the fiber's chemical compositions include color, opacity, strength, permanence, and electrical properties.
In the manufacture of paperboard, barrier coatings are often required to improve resistance to the passage of water, water vapor, oxygen, carbon dioxide, hydrogen sulfide, solvents, greases, fats, oils, odors, recycled contaminants or other miscellaneous chemicals through the paperboard material. Water (liquid) barriers are known and can change the wetability of the paper surface using sizing agents. A grease or oil barrier can be provided by hydrating the cellulosic fibers to form a pinhole free sheet or by coating the paper with a continuous film of a material that is fat or grease resistant (lipophobic). Gas or vapor barriers are formed using a continuous film of a suitable material that can act as a barrier to the specific gas or vapor. Paperboard is also often coated or printed to improve lifetime and utility.
A variety of film materials have been developed as barriers to the passage of water vapor, oxygen or other permeants. Brugh Jr. et al., U.S. Pat. No. 3,802,984, teach moisture barriers comprising a laminate of a cellulosic sheet and a thermoplastic material. Dunn Bolter et al., U.S. Pat. No. 3,616,010, teach a moisture barrier comprising a laminated and corrugated paperboard and a lamination layer of a thermoplastic bag stock. Brugh Jr. et al., U.S. Pat. No. 3,886,017, teach a moisture barrier in a container comprising a laminate of high and low density cellulosic sheets within thermoplastic film. Willock et al., U.S. Pat. No. 3,972,467, teach improved paperboard laminates for containers comprising a laminate of paperboard polymer film and an optional aluminum foil layer. Valyi, U.S. Pat. No. 4,048,361, teaches packaging containing a gas barrier comprising a laminate of plastic cellulosic and other similar materials. Gibens et al., U.S. Pat. No. 4,698,246, teach laminates comprising paperboard polyester and other conventional components. Ticassa et al., U.S. Pat. No. 4,525,396, teach a pressure resistant paper vessel comprising a barrier film laminate having gas barrier properties prepared from paperboard thermoplastic films, paper components and other conventional elements. Cyclodextrin materials and substitute cyclodextrin materials are also known.
Further, Pitha et al., U.S. Pat. No. 5,173,481 and "synthesis of chemically modified cyclodextrins," Alan P. Kroft et al., Tetrahedron Reports No. 147; Department of Chemistry, Texas Tech University, Ludwig, Tex., 79409, USA, (Oct. 4, 1982), pp. 1417-1474. Pitha et al. disclose cyclodextrins and substituted cyclodextrins. The major use of cyclodextrin materials is in formation of an inclusion complex for the delivery of an inclusion compound to a use locus. The cyclodextrin material has a hydrophobic interior pore that is ideal for complexing a variety of organic compounds. Unmodified cyclodextrin inclusion complex materials have been used in films, see Japan Patent Application No. 63-237932 and Japanese Patent Application No. 63-218063. The use of cyclodextrin inclusion compounds is discussed in detail in "Cyclodextrin Inclusion Compounds in Research and Industry", Willfrom Saenger, Angew. Chem. Int. Ed. Engl., Vol. 19, pp. 344-362 (1980). The cyclodextrin inclusion compounds are used in a variety of delivery applications. Materials including deodorants, antibacterial materials, antistatic agents, eatable oils, insecticides, fungicides, deliquescent substances, corrosion inhibitors, flavor enhancing compounds, pyrethroids, pharmaceutical and agricultural compounds, etc. can be delivered. Such applications are disclosed in a variety of patents. Exemplary patents include Shibani et al., U.S. Pat. Nos. 4,356,115; 4,636,343; 4,677,177; 4,681,934; 4,711,936; 4,722,815; and others. Yashimaga, JP 4-108523, teaches a permselective membrane used for separation of chiral compounds using a polyvinyl chloride film containing high loadings of a substituted cyclodextrin and a plasticizer. Yoshenaga, JP 3-100065, uses an unsubstituted cyclodextrin in a film layer. Nakazima, U.S. Pat. No. 5,001,176; Bobo Jr. et al., U.S. Pat. No. 5,177,129; and others use cyclodextrin materials to act as an inclusion complex for film stabilizing components. Zejtli et al., U.S. Pat. No. 4,357,468 shows one specific application of the use of cyclodextrin materials as servants in separation techniques. The particular cyclodextrin material is a polyoxyalkylene substituted material used in separation schemes.
Many alleged barrier materials have been suggested in the art but currently there is no suitable material that can act as a barrier for the large variety of potential contaminants that can pass through packaging materials into the contents of the package. Further, the packaging material itself can be a source of permeants. Many paperboard materials, particularly those containing recycled fibers can contain significant levels of volatile contaminants. Certain food products are especially susceptible to absorbing volatile organoleptic chemicals. These foods include milk and other liquids stored within paperboard cartons, breakfast cereals and crackers comprising grain products, and confectionary products containing chocolate. Candies including chocolate and the high fat confectionaries can absorb larger proportions of off flavors. Absorption of these volatiles can mean a shortened shelf-life and reduced sensory quality. The contaminants are derived from chemical components used in paper product manufacture and comprise a component of an ink, an adhesive, a coating, a filler, a sizing, a binder, a polymer, a lubricant, a preservative, a process aid, etc.
Accordingly, a substantial need exists for the development of new paperboard materials or laminates from virgin fiber, recycled fiber or mixtures thereof. The paperboard contains a barrier layer that can act both as a barrier to the passage of contaminants and as a trap for contaminant materials that can arise in new materials or from the recycle of fiber in the manufacture of paperboard.